N-Doped Carbon Fiber-Encapsulated CoS₂/SnS₂ Heterostructures Facilitate Polysulfide Conversion for Lithium–Sulfur Batteries

Abstract

Heterojunction structures as an advanced strategy may promote the synergistic effect of different component materials; the rational design of heterojunctions allows them to exhibit various advantages when applied to lithium–sulfur batteries. Hollow CoSn(OH)6 was used as a precursor, and polyacrylonitrile PAN and sulfur powder were used as raw materials. N-doped carbon nanofiber-encapsulated CoS2/SnS2 heterostructured materials CoS2/SnS2@CNFs were prepared by an electrostatic spinning technique and in situ vulcanization and applied to the lithium–sulfur battery cathode. A hollow cubic material with structural stability and a physical domain-limiting effect, that is, the CoS2/SnS2 heterostructure, was effectively constructed, and rapid charge transfer was realized by a built-in electric field induced to form by the heterogeneous interface. Meanwhile, the fiber-like network structure facilitates the wetting of the electrolyte and shortens the ion transfer path. The results show that a CoS2/SnS2@CNFs@S-based battery exhibits an excellent electrochemical performance. The initial discharge specific capacities were 1204.3 mAh g–1 at a current density of 0.1 C and 615.2 mAh g–1 at 4 C. The long-cycle performance showed that the cells only exhibited an ultralow decay rate of 0.067% per week on average after 1000 cycles at 2C. When the sulfur loading was increased to 5.3 mg cm–2 and the electrolyte/sulfur ratio was 6 μL mg–1, excellent cycling stability was still demonstrated after 250 weeks of cycling at 0.2C.